1. Field of the Invention
The present invention relates to a pattern data preparing method used in a charged particle beam drawing apparatus that prepares a micropattern with a charged particle beam and, more particularly, to a pattern data preparing method of obtaining highly reliable pattern data.
2. Description of the Prior Art
Along with the development of LSIs, patterns used in semiconductor devices continue to shrink rapidly in feature size. The charged particle beam drawing method using a charged particle beam is an effective method capable of forming a pattern with a size of 0.25 .mu.m or less which will be needed in the future. As a charged particle beam drawing apparatus, a variable shaping type electron beam drawing apparatus as shown in FIG. 1 is used. According to this apparatus, an electron beam is shaped to have a rectangular spot with a first aperture 3 and a second aperture 6. A resultant electron beam 50B is radiated onto a semiconductor wafer 11 coated with a resist, thereby forming a micropattern.
Referring to FIG. 1, an electron beam 50 emitted from an electron gun 1 passes through a blanking electrode 2, the first aperture 3, a shaping lens 4, a shaping deflector 5, the second aperture 6, a reduction lens 7, a main deflector 8, a sub-deflector 9, and a projection lens 10 to irradiate the semiconductor wafer 11 on a stage. A square opening 3A is formed in the first aperture 3 to form a rectangular beam 50A. The rectangular beam 50A passes through an opening 6A of the second aperture 6 to have a small-size square beam spot. Shot (one exposure operation) is repeated with this small-size electron beam 50B to form one latent image pattern in the resist on the semiconductor wafer 11.
A storage unit 15 stores figure data. The figure data is read by a computer 14 and temporarily stored in a figure data memory 17. The drawing apparatus reads this figure data as required, converts it into a control signal with a controller 16, and controls the blanking electrode 2, the shaping deflector 5, the main deflector 8, and the sub-deflector 9 to draw a figure. This figure data is obtained by subjecting CAD data to overlapping removal, proximity effect correction, and the like and converting the resultant CAD data into a specific format for the drawing apparatus. Japanese Unexamined Patent Publication No. 7-288224 describes a method that uses interlayer calculation in order to prevent occurrence of deformation of the pattern on the cell boundary when enlargement and reduction are performed while retaining the hierarchical cell structure. Japanese Unexamined Patent Publication No. 4-372155 describes a method of comparing and verifying the LSI layout pattern, outputting the coordinates of different points, and correcting the layout pattern by using an editor.
In recent years, as the integration degree of semiconductor devices as objects on which patterns are to be drawn increases, the number of patterns to be drawn becomes very large, and the amount of data handled by the conversion software also increases very much. For this reason, batch processing is widely performed. More specifically, a semiconductor chip is divided, and conversion is performed in units of batch process regions. After conversion for all the regions is ended, obtained data are combined to prepare 1-chip data. When this batch processing is performed, it is difficult to handle a pattern crossing the boundary or boundaries between more than one region. Sometimes pattern losses, generation of a redundant pattern, or positional shifts may occur in the data after conversion. If data having such a defect is directly used for drawing, it produces interconnect disconnections, short-circuits, or the like to lead to a decrease in yield of devices. Therefore, it is important to verify whether converted data is different from the original CAD data. Japanese Unexamined Patent Publication No. 7-288224 provides no means for verifying such defects of the pattern data. According to Japanese Unexamined Patent Publication No. 4-372155, the layout pattern is directly corrected with reference to the coordinates of different points, and the corrected data is converted into drawing data again. Accordingly, a very long process time is required to obtain normal drawing data. Since correction is manually performed by the operator, a new defective portion may be undesirably formed during the course of correction.